1. Field of the Invention
This invention relates generally to trommels comprised of a number of individual screen units which collectively form a revolving, drum-like sieve, and pertains more particularly to the construction of a screen unit, the various screen units being structurally identical.
2. Description of the Prior Art
Trommels, of course, are old and well known, comprising a number of individual screen units. Each unit contains a screen in the form of a panel having holes therein of a size and spacing appropriate for the material to be processed.
Some prior art units have utilized an elastomeric panel as the screen, such as polyurethane. However, owing to the resiliency of polyurethane panels, such panels flex outwardly during the rotation of the trommel, and because of this shortcoming some reinforcement has been required in the past. More specifically, the reinforcement has usually involved the employment of steel hardward cloth held against the panel's outer surface so as to resist the outward bulging of the elastomeric panel.
However, the effective anchoring of the hardware cloth along its marginal edges has posed a problem. Even when firmly anchored at its edges, the center of the hardward cloth, which is unsupported, has a tendency to bulge. Also, the hardware cloth, being composed of a grid of criss-crossing wires, is subject to wear caused by the abrasive character of the particulate material being sifted, and therefore must be replaced from time to time. Corrosive environments can also render the screen unit short-lived.
Irrespective of the cause, when hardward cloth must be replaced, it is time consuming and tedious to do so, requiring that the trommel be inactivated or shut down for a period sufficient to permit the change to be made. Also, hardware cloth, and other types of metal reinforcement, adds to the weight of the trommel. Still further, hardware cloth has a propensity for becoming blocked from small rocks, thereby reducing its effectiveness; here again, the removal of the rocks takes time.